Meeting camshaft design specification within an engine is critical in order to provide proper operation of the apparatus driven by that engine. Thus, each manufactured camshaft is tested to make sure critical dimensions are within a desired tolerance. The camshaft journals (round portions of the camshafts located between the cams, are typically checked for proper diameter, roundness and runout (the amount the journal deviates from the camshaft axis or another reference when rotated).
Commonly, the diameter of the journal is measured using an air snap gauge. This gauge includes two arms, each with a straight section and an inwardly angling section, that extend along either side of the journal. The snap guage is advanced over the journal until the journal contacts a pad on the inner side of the inwardly angling section of each arm. When the journal contacts the two pads, slits on the straight section of each arm, are aligned on diametrically opposite side of the journal. By measuring the air resistance encountered as a jet of air is blown through each slit, a reading is obtained that can be used to calculate the journal's diameter.
Alternatively, the diameter is measured by two individual transducer pointer style contact gauges that are precisely positioned on diametrically opposite sides of the journal. Drawbacks to the existing measuring process using the two pointer gauges for measuring diameter are: 1) The pointer contacts must be precisely placed on the journal centerline to achieve repeatable results. This is difficult to do because pointer gauge location is controlled by an advance/retraction system mounted to a machine table (as opposed to the air gauge position that is controlled by resting (in a datum condition) on the actual journal being measured). 2) The accuracy of the pointer gauges is susceptible to variations in the ambient temperature. 3) Two transducers must be used to measure diameter rather than one (as with an air gauge). This introduces twice the error potential from calibration of each gauge.
Unfortunately, an air snap gauge cannot be used to measure runout because of the basic design of the gauge. One of the reasons the air snap gauge is very accurate is because it rests (datum condition) on the journal being measured, thus, keeping the air gap consistent between the two arms of the gauge and the journals. As the part is rotated, the air snap gauge will move with the part keeping the air gap between the arms and the journals consistent. Since the air gap is consistent and doesn't vary with the rotation, the air resistance measured by the gauge doesn't change with the part rotation. Thus, meaningful runout measurements readings cannot be obtained with the air snap gauge.
Runout may be measured manually using a single pointer gauge, positioned differently from the two pointer gauges used to measure diameter. The single pointer gauge is brought into contact with the journal and then read as the camshaft is rotated between centers. Typically, the camshaft is placed on a table stand, the pointer gauge manually aligned, and then runout measurements are made.
As a result, the diameter and runout are conventionally measured in two separate steps, often at two different locations, which increases the time of the overall measuring process. Therefore, there exists a need in the art for an assembly that can measure journal size, roundness, and runout, and for such an assembly that can be easily set up.